XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Giant SAC-CI Method : Aperiodic System
H. Nakatsuji and T. Miyahara
Quantum Chemistry Research Institute and JST CREST
The SAC/SAC-CI method is a useful established coupled-cluster type method for studying ground, excited, ionized and electron attached states of molecules [1-3]. It is widely distributed through Gaussian09 [4]. Giant SAC-CI method [5] is designed to calculate giant-size molecular systems with the same accuracy as the ordinary SAC-CI method of small molecules. We want to realize seamless applicability of the SAC-CI method from small to large and even to giant-size molecular systems.
Previously, our applications of the giant SAC-CI method were mainly to regular periodic systems. We here apply this method to aperiodic systems. We first apply it to an oligomer of glycine as a model of protein. The n→π* excitation energy of each C=O of glycine is different depending on its position and environment in the oligomer. Glycine does not give circular dichroism but glycine oligomer gives and the rotatory strength is dependent on the position of the monomer in the oligomer. These facts suggest that a combination of the usage of SAC-CI and very fine experiment may help to lead to a deeper understanding of the structure of proteins.

References
[1] Nakatsuji, H. Chem. Phys. Lett.1978, 59, 362.; 1979, 67,329,334; Bull. Chem. Soc. Jap. 2005, 78, 1705.
[2] SAC-CI homepage. http://www.qcri.or.jp/sacci/ (6/6/2005)
[3] Ehara, M.; Hasegawa, J.; Nakatsuji, H. Theory and applications of Computational Chemistry, The First 40 Years, Elsevior Oxford, 2005; p1099.
[4] Frisch, M. J.; et at. GAUSSIAN 09, Gaussian, Inc. Wallingford CT, 2009.
[5] H. Nakatsuji, T. Miyahara, R. Fukuda, J. Chem. Phys. 2007, 126, 084104


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